This invention relates to means for locking the soft jaws of a chuck, such as a lathe chuck or the like, during the procedure for machining the jaws to fit the workpiece to be held by the jaws of the chuck.
In three-jaw lathe chucks, each soft jaw is secured on top of a hard jaw of the chuck and all the soft jaws can be machined by the rotation of the chuck mounted on the spindle of the lathe. Within the past ten years, the computer numerical controlled turning centers have come into widespread use worldwide. Such devices are extremely accurate and produce parts faster and with much better finish than was heretofore possible. The introduction of these devices caused chuck manufacturers to make chucks which require much greater holding pressure per jaw. For example, most of the power chucks available today are hydraulic and involve a holding pressure per jaw which could exceed 10,000 p.s.i. This high pressure is required to hold the parts of the jaws securely so as to withstand the high RPM of the computer numerical controlled machining centers in use today.
However, there are no devices available in the prior art that can lock the soft jaws for the purpose of machining the jaws to fit the workpiece at full chuck pressure and that provides for adjustment of the jaws in locking position for the exact amount of metal removal desired.
A satisfactory locking device of the indicated type must be able to make accurate adjustment for the purpose of machining the exact amount of metal from the jaws so that the jaws fit the workpiece to be held thereby within a tolerance of plus or minus 0.0005 inches, and must be able to stop the jaws within the movement of the chuck attaining the maximum jaw pressure that can be delivered by the chuck. Further, such a device should enable the operator to use a setup method that requires a minimum of time and that eliminates the need to machine steel plugs or the use of spiders, which method could reduce the average setup time from 1.5 hours to 15 minutes. Further, such a device must provide some means for the operator to know how much metal he is going to remove during a jaw machining operation. Furthermore, the device must be able to stop the jaws in measured thousandths of an inch. Also, the device must be safe at all times and must be retained securely on the chuck during the machining operation. Furthermore, the device must allow the operator to machine the front of the jaws as well as the internal diameter and be able to bore completely through all of the jaws, typically three.
It is the general object of the invention to provide a jaw locking device which achieves all the requirements set forth immediately above. Briefly stated, the jaw locking device in accordance with the invention comprises a ring adapted to be arranged to encircle the soft jaws, the ring having radially extending holes adapted to be aligned with the axis of radial movement of said soft jaws. The device also includes a plurality of studs, with one stud being secured to and extending outwardly from each of the soft jaws along the axis of radial movement thereof. Each stud extends through an associated radial hole in the ring to extend radially outwardly from the outer surface of the ring and is provided with an externally threaded portion extending outwardly of the ring. The device also includes a plurality of nuts, one nut being threadedly engaged on the threaded portion of said studs. In accordance with the invention the nuts are adjustable axially along the studs to a position to limit the radial inward movement of the soft jaws to thereby locate said soft jaws at a desired position for the machining of the workpiece engaging surfaces on said soft jaws.